Concentrated aqueous solutions of alkali and alkaline earth metal salts of phospho-organic compounds



States This invention relates to new liquid compositions for use as promoters or collectors in the froth flotation of sulfide ores.

Technical grade alkyl diesters of dithiophosphoric acids and their hydrolysis products have been heretofore used as flotation promoters and collectors for base metal sulfide ores and precious metal ores. These compounds, however, have presented serious problems. In the form of their free acids they are corrosive and cannot be handled safely in metal drums. Many attempts have been made to solve this problem.

One approach, was to prepare concentrated aqueous solutions of ammonium salts of the dialkyl dithiophosphoric acids. See for example, U.S. Patent 2,206,284. Water solutions of the ammonium salts of dialkyl dithiophosphoric acids, even those containing excess ammonium hydroxide are only temporarily stable. These solutions, upon standing, decompose, apparently liberating the corrosive free acid and gaseous decomposition products which cause rupture of the metal storage containers. They are thus unsatisfactory where it is desired to store the reagents for longer than a few weeks.

A later proposal was to prepare stoichiometrically neutralized salts of the alkyl diesters of dithiophosphoric acid, using alkali metal hydroxides or carbonates for the neutralization. Salts thus formed, while relatively noncorrosive, are melting gels or pastes which are difficult to dry. Moreover, after drying, these salts are not easily soluble. They form hard concretions which cannot be added directly to a froth flotation circuit.

It was attempted to obtain these alkali salts in a dry form which would be easily dissolved and yet not present corrosion problems. One method used to obtain such dry compositions was to neutralize the alkyl diesters of dithiophosphoric acids with an alkali metal base, such as the alkali-metal carbonates, followed by heating with a large excess of the same alkali-metal base to obtain a final dry mixture of solids. These dry mixtures also have several disadvantages. They are diluted in active ingredients and the large excess of alkali required to keep the ester stable in dry form increases the cost without a corresponding improvement in efliciency as a flotation collector. These dry'promoters, particularly those containing large quantities of alkaline carbonates have another disadvantage in that excess carbonate forms precipitates in hard water. This interferes with the feeding of these reagents to flotation operations.

An even further disadvantage accompanies the use of such dry products. The alkyl diesters of dithiophosphoric acids result from the reaction of a phosphorus sulfide, such as phosphorus pentasulfide, with a hydroxylcontaining organic compound, such as a primary or secondary alcohol. The resulting product mixture contains not only the alkyl diesters of dithiophosphoric acids but also minor amounts of the alkyl diesters of monothiophosphoric acids and variable amounts of oily trialkyl esters.

These triesters are also excellent flotation promoters. Not being acidic in character, they are not neutralized by the above-mentioned treatments with alkali. As a result, they are usually distilled off and lost in the drying process.

3,685,653 Patented Apr. 23, 1953 The final dry product is deprived, wholly or in part, of a valuable flotation promoting component. If the proportions of such oily components is large and they are present during and after the above-described drying treatment, they interfere with drying by producing oily pastes which after drying are diflicult to handle, dissolve and feed. In some cases it is necessary to dissolve the neutralized product in Water, to remove the oily components by extraction with solvents such as toluene, and then to recover the alkali metal salts by evaporation of the Water.

Flotation operators frequently prefer to use a mixture of the sodium salts of the alkyl diesters of dithiophosphoric acids in the flotation of various ores. Preparation of these salts by neutralizing blends of such acids, even using the excess alkali as described above, is diflicult. The low melting points of such neutralized mixtures cause formation of pasty products resulting from the alkali treatment. These difliculties, in many instances, have prevented the practical use of such mixed reagents. This problem is particularly acute, when attempts are made to prepare these salts from mixtures of isomeric alkyl diesters of a particular dithiophosphoric acid ester such as, for example, the isomers derived from mixed amyl alcohols which are produced commercially in large quantities and these are readily available. This diificulty has prevented the practical use of low cost starting materials which are known to produce .eflici'ent promoters for various ores and has forced operators to use higher priced raw materials.

Nevertheless, these dry mixtures of the diester and alkalies has been in commercial use for lack of a more desirable replacement.

It is an object of this invention to overcome the aforementioned difliculties in the use of alkyl diesters of dithiophosphoric acids and their hydrolysis products for flotation promoters and collectors by the provision of a relatively inexpensive composition of matter, though storagestable, and non-corrosive, is nevertheless easily used and highly eflicient.

- In general, these objects are accomplished in accordance with this invention, by the provision of a composition comprising an aqueous solution of (1) neutralized P S -alkanol reaction product, or the neutralized partial hydrolysis products thereof, and (2) an alkali metal base in an amount of about 10 to 25% of that required to form the neutral salt. These compositions, While stable and non-corrosive, contain at least 40% of the active thiophosphoric acid ester component and only a small amount of excess alkali metal base. Thus, the cost of the solution is kept at a minimum because of a loW proportion of inerts, while its efliciency is high due to the high con centration of the dithiophosphoric acid component.

Starting materials of the composition of this invention are prepared by a conventional reaction of lower alkanols and phosphorous pentasulfide. As noted above, minor quantities of such side reaction products as monothiophosphoric acid and oily compounds such as esters of monoand dithiophosphoric acids are included in the technical grades of alkyl esters of dithiophosphoric acids as thus conventionally prepared. Suitable compounds are alkyl dithio-phosphoric acid esters wherein the alkyl groups preferably have less than 6 carbon atoms, such as diethyldithiophosphoric acid, diisopropyldithiophosphoric acid, di-sec.butyl-dithiophosphoric acid, mixed ethyl and secondary butyl dithiophosphoric acids and other such mixltures, and also mixed isomeric dialkyldithiophosphoric aci s.

Partial hydrolysis products are prepared in accordance with the disclosure of U.S. Patent 2,919,025. These hydrolysis products are mixtures of unhydrolyzed dialkyl dithiophosphoric acid, dialkyl monothiophosphoric acid 3 v and comparatively smaller and varying amounts of the neutral 0,0,0-trialkyl monothiophosphate and 0,0,S- trialkyl dithiophosphate.

To prepare aqueous solutions of this invention the P S -alkanol reaction product, or the partial hydrolysis products thereof, is titrated With a base, e.g., 0.1 normal sodium hydroxide, to determine the total acid content. Then a solution of soluble alkali, e.g., sodium hydroxide, potassium hydroxide, sodium carbonate and potassium carbonate containing the stoichiometric quantity of alkaline base plus from -25% excess, is prepared. To this suspension or solution, as the case may be, is added the acidic products prepared as hereinabove described. Agitation should accompany the addition. When addition is complete, the neutralized product containing from 10- excess alkaline metal base is filtered, if required, thus yielding the aqueous solutions of this invention.

Solutions containing from 40-60% of the neutralized thiophosphate are readily prepared by the above method. Water is, of course, produced during the neutralization process and should be accounted for in preparing the solutions of any desired concentration. In other words, the final water content is the sum of the Water added plus the water formed during neutralization. The rate of neutralization is not critical but by-product production is kept to a minimum if the temperature during neutralization is not allowed to exceed 50 C.

The aqueous solutions of the invention are stable in storage over long periods as compared to stoichiometrically neutral solutions, i.e., those not having excess base. Furthermore, the concentrated solution of the present invention obviates all the above-listed difliculties encountered in storage and shipping, the problems and cost of the drying operations, the inconveniences caused by precipitate formation in hard water, and the decrease in flotation efliciency due to loss of the triester component in processing. Even if the triester content of the alkyl diesters of thiophosphoric acids is high, this factor does not interfere with the formation of and impair the stability of the concentrated solutions of this invention because the high concentrations of the soluble alkali metal salt of the alkyl diester solubilize such oily components to form solutions from which no reprecipitation occurs until the composition is made very dilute for feeding to flotation. In such cases the oily triesters form extremely fine dispersions which are in a readily available form along with the soluble components to act conjointly on mineral particles and thus render them amenable to flotation.

In addition, this invention allows the use of mixtures of isomers of the same alcohol and mixtures of different alcohols as starting materials, since the resulting acidic products are readily neutralized to form stable solutions, which are useful as flotation agents.

Aqueous solutions of the present invention can be used as such in froth flotation and can be fed directly to flotation operations with or without being first diluted with water. In any event, being effective collectors in both acidic and alkaline circuits, they are suitable for use in concentrating sulfide, oxidized and oxide minerals from ores of such base metals as those of copper, lead, zinc, and iron and also ores of precious metal. If diluted for addition to flotation circuits, they can be used conveniently in concentrations from as low as about 0.3% or as high as from 25% to about 50%, as desired. Direct use without dilution also may be practiced and saves the cost and labor of preparing solutions, which is usually required in flotation practice.

The following examples are presented to more fully i1- lustrate the present invention. Parts and percentages'are expressed on a Weight basis unless otherwise stated.

Example 1 To 202.9 parts water containing 48 parts sodium hydroxide are added 215.8 parts of technical grade diethyldithiophosphoric acid (86.2%), prepared by reacting 4 molal parts of anhydrous ethyl alcohol to- 1 molal part of phosphorus pentasulfide. The mixture is agitated and maintained below 50 C. during the addition of the acid, and then filtered. Water amounting to 18 parts is formed during neutralization, yielding an aqueous solution containing 48.5% of the sodium salt of diethyldithiophosphate and 20% sodium hydroxide.

Resultant solution is storage-stable in a steel container without substantial change even after a period of six months.

Example 2 By the method described in Example 1, concentrated aqueous solutions of the sodium salts of various alkyl dithiophosphoric acids were prepared as summarized in the following table.

Dithio Acids Used Parts Added Percent Sodium Dialkyl Per- Water Dlthio- Type cent Parts N 8011 phosphate Active in Final Solution Di-isopropyl 92. 0 232. 6 48 199. S 52 Di-sec. butyl 91. 7 263. 9 48 246. 0 50 Di-normal propyl- 92. 0 232. 6 48 199. 8 52 Di-normal butyl. 91. 7 263. 9 48 246. 0 50 Di-isopropyL 92. O 232. 6 48 139. 3 60 Di-sec. but 91. 7 263. 9 48 158.0 60 Di-isopropyl. 92. 0 232. 6 44 175. 0 55 Di-sec. but 91. 7 263.9 46 198.0 55 Di-ethyl 86. 2 215. 8 48 312.0 40 Di-amyl 92. 3 292. 5 50 420. 8 4O 1 18 parts of water formed in each neutralization. Resulting solutions containing 10-25% alkah were found storage-stable over a period of six months.

Example 3 By the method used in Example 1, concentrated aqueous solutions of potassium salts of various alkyl dithiophosphoric acids were prepared as summarized in the following table.

These solutions were found to be storage-stable for six months.

Example 4 The procedure outlined in Example 1 was followed using 263.9 parts of disecondary butyldithiophosphoric acids (91.7%), 63.6 parts of sodium carbonate and 246 parts of added water. A 50% solution of the sodium salt resulted.

Similarly, a 50% solution of the potassium salt of diethyldithiophosphoric acids was prepared, using 69.1 parts of potassium carbonate, 215.8 parts of diethyldithiophosphoric acid (92%), and 206 parts of added water.

Both the above solutions contained 20% free alkali and were storage-stable at room temperature in tests over a six months period.

Example 5 A 47.5% solution of mixed sodium salts of diethyl and disecondary butyl dithiophosphoric acids was prepared by adding 215.8 parts of diethyldithiophosphoric acids (86.2%) and 208.0 parts of disecondary butyl dithiophosphoric acids. (91.7%) to 427.6 parts of water containing 85.8 parts sodium hydroxide. The method used was similar to that described in Example 1 and the final solution contained 20% sodium hydroxide.

A 40% solution of the sodium salts of the diamyldithiophosphoric acids prepared from commercial mixed primary amyl alcohols was made by the above method, using 292.5 parts of these acids (92.3% by titration), 50 parts of sodium hydroxide and 420.8 parts of added water.

Likewise a 45% of the sodium salts of the diamyldithiophosphoric acids prepared from a commercial mixture the primary and secondary amyl alcohols was made by the above method, employing 312.5 parts of these acids (86.4% by titration), 49.5 parts sodium hydroxide, and 420.8 parts of water.

Samples of the resultant solutions were subjected to six month storage tests without deterioration.

Example 6 The hydrolysis products of diethyldithiophosphoric acid were prepared as described in Example 1 of US. Patent 2,919,025 and contained a mixture of approximately 1 part of diethyldithiophosphoric acid and 1 part of diethylmonothiophosphoric acid together with small amounts of 0,0,8- and 0,0,0-trialkyl esters of these acids. This preparation was titrated and found to have an equivalent weight of 248. To 200 parts of this composition were added slowly 41 parts sodium hydroxide in 49 parts water, a 25% excess of sodium hydroxide over that required to neutralize the acids. During the addition of alkali, the mixture was maintained under agitation and kept below 50 C. The resulting solution was filtered to yield a yellow solution containing 55% of the combined diethylmonoand dithiophosphoric acids as sodium salts. The oily triesters are readily soluble in this solution which was non-corrosive to steel drums and storage-stable over a six month period.

Example 7 Several of the products prepared in previous examples were used as promoters for the copper minerals contained in porphry copper ore from the Western United States. In separate tests, this ore was ground at 60% solids to about minus 65 mesh in the presence of 1.2 pounds per ton of lime and 0.03 pound per ton of sodium cyanide, then diluted to 22% solids and conditioned for a total of 2 minutes with 0.025 pound per ton of promoter, and 0.08 pound per ton of pine oil frother, and floated 4 minutes in a laboratory Fagergren flotation machine to remove a copper concentrate. The concentrated solutions of the various neutralized dialkyldithiophosphate esters were fed directly to conditioning without dilution. A copper concentrate and a flotation product were produced in each test and these were assayed for copper. The following table summarizes the results of these tests.

Copper Dialkyldithiophosphate Concentrate,

Percent Copper Concen- Source Type tration in Assay Recovered Example Solution,

Percent 48. 5 13. 33 92. 99 52 15. 93. 57 50 17. 47 93.08 50 17. 43 93. 12 60 17.40 40 13. 45 50 13. 79 45 17.09 50 13.69 50 13. 86 Mixed Diethyl and Di- 47.5 13. 37 93.77

sec. butyl. 5 Mixed Primary Amyl..- 40 13. 10 93. 83

1 Potassium salts; all other promoters were sodium salts.

As may be seen from these illustrative results, direct use of the solutions, without further dilution, produced excellent copper recoveries in all cases.

Example 8 The solution of the neutralized hydrolysis products of diethyldithiophosphoric acids prepared in Example 6 were used as promoters for the flotation of three different copper ores. The promoter was fed directly as the original concentrated solution without further dilution. The methods employed and the metallurgical results are summarized as follows.

A South American copper-molybdenum ore containing about 1.90% Cu and 0.07% M08; was ground at 60% solids and conditioned at 22% solids with 0.2 pound per ton of the neutralized hydrolysis product, 4.0 pounds per ton of sulfuric acid, and 0.15 pound per ton of cresylic acid as frother. The ore was then floated at about 22% solids for 10 minutes to produce a copper-molybdenum concentrate, assaying 22.42% Cu and 0.47% M08 and representing a recovery of 86.6% of the copper and 53.7% of the molybdenum. The flotation tailing assayed 0.28% Cu and 0.032% M08 A copper ore from the Western United States containing a variety of sulfide copper minerals closely associated with pyrite and various oxide copper minerals was ground and conditioned for 6 minutes with 7.0 pounds per ton of lime, conditioned for 2 minutes at about 22% solids with 0.06 pound per ton of methylisobutylcarbinol as frother and as promoter 0.075 pound per ton of the neutralized hydrolysis product, and floated for 10 minutes. From a flotation feed assaying 0.99% On, a concentrate was produced, which assayed 16.41% Cu and contained 87.63% of the total copper.

A copper ore fromthe Western United States, containing 0.91% Cu as combined sulfide and oxide copper was ground and subjected to leaching with sulfuric acid after which the soluble copper was precipitated on sponge iron and the combined sulfide and precipitated copper floated together as a single concentrate. As flotation promoter 0.17 pound per ton of the neutralized hydrolysis product was used along with 0.13 pound per ton of pine oil as frother. The flotation time was 5 minutes. The pH of the flotation pulp was 4.1. The resulting flotation concentrate assayed 22.43% Cu and contained 87.69% of the total copper contained in the original ore.

Example 9 Four flotation tests were conducted on a zinc ore from the Southeastern United States, containing about 3.5% Zn as zinc sulfide with a small amount of oxide zinc minerals. These tests utilized as promoters solutions of the various dialkyldithiophosphoric acid esters prepared in previous examples. This ore was ground at 60% solids to about minus 65 mesh in particle size, conditioned with 1.0 pound per ton of copper sulfate, 0.12 pound per ton pine oil frother and 0.1 pound per ton of the neutralized diester, diluted to about 0.3% in concentration for feeding to the conditioning operation. The following table summarizes these tests.

Diester as Promoter Zinc Concentrate,

Percent Zn Source Concentra- Example Type tion In Assay Recovered Solution 1 Dicthyl (hydrolyzed). 55 46.78 98. 50 Di-isopropyl 52 46.47 98.68 Mixed Diethyl and sec. 47. 5 46. 39 98. 35

Butyl. 3 Dlethyl- 50 47.01 98.44

1 Before dilution for feeding. 2 Potassium salt; other promoters as sodium salts.

Example 10 A tristate lead ore containing 55% lead mainly as lead sulfides, was ground to about minus 65 mesh, conditioned for 2 minutes and floated for 5 minutes to recover a lead concentrate. Three flotation tests were conducted. The first employed 020 pound per ton of creosote oil and 0.06 pound per ton of mixed amyl alcohols as frother and 0.2 pound per ton of the 40% solution of the neutralized mixed primary diamyl esters of Example 5' as Promoter. The second test was conducted similarly except that 0.20 pound per ton of the 55% solution of the neutralized hydrolysis product prepared in Example 6 was the promoter. The third test was also conducted similarly except that 0.20 pound per ton of the 45% solution of the potassium salt of the disecondary butyl ester prepared in Example 3 was used as promoter. The following results were obtained.

This invention may be otherwise embodied within the scope of the appended claims.

I claim:

1. A storage-stable flotation promoter essentially comprising an aqueous solution of (1) at least 40% by weight of at least one neutral salt of a member selected from the group consisting of (a) a P S -alkanol reaction product and (12) its partial hydrolysis products; and (2) free alkali metal base in an amount of 10 to 25% by weight of that required to form said neutnal salt.

' 2. The composition of claim 1 wherein the alkali metal base is sodium hydroxide.

3. The composition of claim 1 wherein the neutral salt is the alkali metal salt of diisopropyldithiophosphoric acid.

4. The composition of claim 1 wherein the neutral salt is the alkali metal salt of di-sec.-butyldithiophosphoric acid.

5. The composition of claim 1 wherein the neutral salt is the alkali metal salt of a mixture of diethyldithiophos-v phoric and di-sec.-butyldithiophosphoric acids.

6. In a process of beneficiating ores by froth flotation in the presence of a dithiophosphate promoter, the improvement which comprises supplying the promoter as an aqueous solution of claim 1.

7. The process of claim 6 wherein the ore is a sulfide ore.

8. The process of claim 6 wherein the ore is a copper ore.

9. The process of claim 6 wherein the ore is a zinc ore.

References Cited in the file of this patent UNITED STATES PATENTS 1,868,192 Buchanan July 19', 1932 1,893,018 'Christmann Jan. 3, 1933 2,206,284 Jayne July 2, 1940 2,838,557 Verley June 10. 1958 2,919,025 Booth Dec. 29, 1959 2,932,614 Lynch Apr. 12, 1960 FOREIGN PATENTS 220,805 Australia Mar. 7, 1957 1,050,330 Germany Feb. 12, 1959 

1. A STORAGE-STABLE FLOTATION PROMOTER ESSENTIALLY COMPRISING AN AQUEOUS SOLUTION OF (1) AT LEAST 40% BY WEIGHT OF AT LEAST ONE NEUTRAL SALT OF A MEMBER SELECTED FROM THE GROUP CONSISTING OF (A) A P2S5-ALKANOL REACTION PRODUCT AND (B) ITS PARTIAL HYDROLYSIS PRODUCTS; AND (2) FREE ALKALI METAL BASE IN AN AMOUNT OF 10 TO 25% BY WEIGHT OF THAT REQUIRED TO FORM SAID NEUTRAL SALT. 